1. Field of the Invention
The present invention relates generally to punching plural holes in a substrate, such as "greensheet", or a metal foil at a high rate of speed. More particularly, an electrical coil is described that has enhanced cooling features, which increases the speed and reliability of the magnetic repulsion punch apparatus, in which the coil is used.
2. Description of the Related Art
Magnetic repulsion technology has been utilized for several years to punch greensheets in order to form multilayer ceramic substrates for use in the computer industry. Briefly, the repulsive forces generated between an energized electrical coil and an electrically conductive punch head, or disk, is used to drive the punch into a dielectric material, thereby forming holes. These holes or vias are then aligned on adjacently stacked dielectric sheets and metallized to form multilayer substrates. More specifically, several configurations of coils have been utilized in magnetic repulsion punches with varying degrees of success.
For example. U.S. Pat. No. 4,821,614, hereby incorporated by reference, describes a wire wound coil that includes plural configurations of spacers, adjacent to the wire, which allow cooling fluid to be circulated radially through the coil. However, it has been found that the mechanical characteristics of wire wound coils will not meet the requirements of a production type magnetic repulsion (M-R) tool, thereby causing extensive down time. It has been determined that this type of coil has an average life of approximately 15 million cycles. Further it can be seen that by creating spaces between the wound wires, less conductive material can be included in the coil such that electrical performance is degraded.
U.S. Pat. No. 4,872,381, hereby incorporated by reference, uses a coil that is photoetched from a flat copper or aluminum sheet. This coil is made from two separate etched pieces and then assembled. Liquid coolant is circulated through the coil. A problem exists with this design, because there is not a sufficient number of turns to provide the necessary magnetic force, nor is the crossectional area of the conductors sufficient to make the impedance acceptably low.
To solve the problems exhibited by the coils in the previous magnetic repulsion tools, a tape wound coil was developed and is described in IBM Technical Disclosure Bulletin, Vol. 33, No. 4, September 1990, pps. 219-220, hereby incorporated by reference. This coil was cooled by exposing one of the generally planar sides of the coil to a coolant. Although providing adequate electrical characteristics, the tape coil was not able to operate at the necessary high frequency due to lack of a sufficient cooling mechanism.
Additionally U.S. Pat. No. 4,209,129 describes a cooling system for the punch head of a solenoid operated punch apparatus. More particularly, coolant is circulated through a manifold chamber to conduct heat away from a punch assembly.
It would be desirable to have a coil for use in a magnetic repulsion punch apparatus that exhibited all of the electrical characteristics of a tape wound coil, but without the cooling problems associated with these types of coils. Further a method of consistently making coils that exhibit these electrical and cooling characteristics would be advantageous.